(a) Field of the Invention
The present invention relates to a polyester sewing thread usable for fabric for an airbag, and a preparation method thereof. In particular, the present invention relates to a polyester sewing thread for an airbag capable of not only having excellent sewing performance when a specific polyester yarn is applied to a fabric for an airbag, but also maintaining packaging of air tightness of an airbag cushion and exhibiting excellent shape stability when the airbag cushion is unfolded.
(b) Description of the Related Art
Generally, an airbag refers to a device to protect drivers and passengers upon a head-on collision of a vehicle driving at a speed of about 40 km/h or more by sensing a collision impact to the vehicle with an impact sensor, and then exploding gunpowder to supply gas into the airbag, thereby inflating the airbag. A structure of a general airbag system is as shown in FIG. 1.
As shown in FIG. 1, a general airbag system is configured to include an airbag cushion module 100 including an inflator 121 generating a gas by ignition of a detonator 122, and an airbag 124 expanded and unfolded towards the driver in a driver's seat by the generated gas, and mounted on a steering wheel 101; an impact sensor 130 generating an impact signal at collision; and an electronic control module 110 igniting the detonator 122 of the inflator 121 by the impact signal. In the airbag system as configured above, when a vehicle collides head-on, the impact sensor 130 senses an impact to transmit a signal to the electronic control module 110. Herein, the electronic control module 110 recognizing the signal, and ignites the detonator 122 to burn a gas generator inside the inflator 121. The thus-burned gas generator inflates the airbag 124 through rapid gas generation. The expanded and unfolded airbag 124 thus contacts the frontal upper body of the driver to partly absorb an impact load caused by collision, and in a case where the head and the chest of the driver move to the front by inertia to collide with the inflated airbag 124, the gas in the airbag 124 is rapidly emitted through an emission hole formed in the airbag 124, and acts as a buffer to the front of the driver. Thus, a secondary injury may be reduced by effectively buffering an impact force transmitted to the driver upon frontal collision.
As described above, the airbag cushion used in a vehicle is prepared in a predetermined shape and is installed in a steering wheel, side windows, or side pillars of the vehicle in a folded state so as to minimize volume thereof. The airbag cushion is fixed to a vehicle body by using a tab portion and the like while being maintained in a folded state, and when the inflator 121 operates, the airbag cushion is expanded and unfolded. Here, even though it is a short time, high temperature gas having a temperature of about 300° C. to 700° C. is generally generated into the airbag by the inflator. Therefore, for the fabric for an airbag such as nylon or the like, a heat resistant polymer layer made of silicone, chloroprene rubber, or the like, is formed at an inner side surface of the fabric for an airbag to protect the airbag from the high temperature gas.
As existing sewing threads for an airbag, a polyamide fiber (nylon 66, nylon 46) sewing thread and an aramid (p-aramid) sewing thread are widely used; however, they are disadvantageous in view of a cost as compared to a sewing thread for an airbag to which a polyester yarn is applied. Currently, the sewing thread to which the polyester yarn is applied is widely used for clothing and industrial products; however, it is not applied to airbag products for protecting passengers in a vehicle upon a vehicle collision accident. The existing polyester sewing thread has limitations in being applied as a sewing thread for an airbag due to low yarn toughness, which is a basic physical property needed for being used as a sewing thread for an airbag, as well as insufficient heat resistance and stiffness as compared to nylon sewing thread. In addition, upon a static test of a cushion manufactured by sewing the existing polyester sewing thread on the airbag cushion, problems such as melting, cutting, deterioration, and the like of the sewing thread by high temperature and high pressure gas of the inflator may occur, and a fabric at a sewing part is also expanded, such that it is not usable for the airbag cushion.
Therefore, research on development of a polyester sewing thread for an airbag capable of having a highly competitive price, excellent sewing performance, and excellent stability even under high temperature and high pressure gas conditions of the inflator when the airbag is unfolded so as to be effectively used for a fabric and a cushion for an airbag is required.